732 THE SPERM WHALES, GIANT AND PYGMY. 
fore proposed to designate the genera Physeter and Kogia 
as representatives of two sub-families of PrysETERIDE, to 
be respectively designated as Puysererinz and Kocuna. 
If we are called upon to make a distinction between sub- 
family and generic characters, it is believed that the most 
important are the form of the head (a difference of greater 
moment than analagous ones among the Delphinide) and 
position of the blow-holes, the form and direction of the 
cerebral cavity and coórdinate modification of its enclosing 
bones; the direction of the occipito-sphenoid axis, and the 
form and relations of the jugal and zygomatic processes of 
the squamosal bones. 
And lest some may entertain a suspicion that some of the 
differences above enumerated may be the result of vegeta- 
tive growth (or bulk) in Physeter, it is proper to add that 
the young of that form essentially resembles the adult, and 
that the characters enumerated are as applicable to the one 
as to the other. Nor are the characteristics of Kogia the 
expressions of arrested development; they are special mod- 
ifications, and the form itself is quite as specialized a type 
as is Physeter itself. Both forms, so far as known, have 
equally lost the evidences of the nature of their common 
progenitor, and it is impossible to decide, from present facts, 
which is the most divergent from the common stock. If we 
were to be guided by consideration of size, Kogia would 
seem to be the most divergent, the typical PAyseterids and 
related Ziphiids being all large animals, but such hint 
would probably be illusive per se, although really perhaps 
near the truth. 
6. Subdivisions of the Family. While the first subdi- 
vision of the family into two subfamilies based on tangible 
and reliable data, is that presented in this article, a binary 
division had been previously proposed by Dr. J. E. Gray, 
in the "Additions and Corrections" of his "Catalogue of 
Seals and Whales in the British Museum," published in 
1866 ; therein (p. 386), he subdivides the family as follows: 
